1. Field of the Invention
The present invention relates to an optical recording medium, as well as an optical recording method and an optical recording device using the optical recording medium.
2. Description of the Related Art
Recordable DVD media have been developed as next-generation optical disks with large capacities. The possibilities of increasing the recording capacity of the DVD media are in the development of a recording material that can minimize a recording pit to be formed, introduction of image compression technologies such as Moving Picture Experts Group-2 (MPEG 2), and improvement in the method of shortening the wavelength of the semiconductor laser used to read the recording pit.
An AlGaInP semiconductor laser with a wavelength of 670 nm is only one red semiconductor laser that has been developed and commercialized for a bar code reader and a measuring instrument. Along with the development of the optical discs with a high recording density, the red semiconductor laser has been introduced and used in practice in the optical recording industry. For a driving system for a digital versatile disc (DVD), semiconductor lasers with wavelengths from 630 to 690 nm are standardized as the light sources. A reproduction-only DVD-ROM drive equipped with a light source with a wavelength of 650 nm or less is now commercially available.
Under these circumstances, most preferred recordable DVD media are media on which information can be recorded and read at a wavelength of 630 nm to 690 nm. Various dye materials such as cyanine dyes, azo dyes, azomethine dyes, styryl dyes, formazan dyes and squarylium dyes have been proposed for use in the recording layer. Examples of these proposals are shown below.
a) Conventional Technologies on Write-once-read-many (WORM) Media
Those using a cyanine dye as a recording material: Japanese Patent Application Laid-Open (JP-A) No. 57-82093, No. 58-56892, No. 58-112790, No. 58-114989, No. 59-85791, No. 60-83236, No. 60-89842 and No. 61-25886
Those using a phthalocyanine dye as a recording material: JP-A No. 61-177287, No. 61-154888, No. 61-246091, No. 62-39286 and No. 63-37991
b) Conventional Technologies on Recordable Compact Disks (CD-Rs)
Those using a cyanine dye and a metal reflective layer as recording materials: JP-A No. 01-159842, No. 02-42652 and No. 02-168446
Those using a phthalocyanine dye and a metal reflective layer as recording materials: JP-A No. 01-176585, No. 03-215466, No. 04-113886, No. 04-226390, No. 05-1272, No. 05-171052, No. 05-116456, No. 05-96860 and No. 05-139044
Those using an azo-metal chelate dye and a metal reflective layer as recording materials: JP-A No. 04-46186, No. 04-141489, No. 04-361088, No. 05-279580, No. 07-161069, No. 07-37272, No. 08-231866 and No. 08-295811
c) Conventional Technologies on Large-capacity Recordable Digital Versatile Disks (DVD-R)
Those using a cyanine dye and a metal reflective layer as recording materials: “Development of DVD-Recordable” and “Fundamental Development of DVD-R”, PIONEER R&D vol. 6, No. 2, 1996; “High Density of Recording on Dye Material Disc Approach for 4.7G”, International Symposium on Optical Memory and Optical Data Storage 1996 (ISOM/ODS '96), 1996; and JP-A No. 10-235999
Those using an azomethine dye and a metal reflective layer as recording materials: JP-A No. 08-198872, No. 08-209012, No. 08-283263 and No. 10-273484
Those using an azo-metal chelate dye and a metal reflective layer as recording materials: Japanese Patent Application Publication (JP-B) No. 05-67438; JP-A No. 07-161069, No. 08-156408, No. 08-231866, No. 08-332772, No. 09-58123, No. 09-175031, No. 09-193545, No. 09-274732, No. 09-277703, No. 10-6644, No. 10-6650, No. 10-6651, No. 10-36693, No. 10-44606, No. 10-58828, No. 10-86519, No. 10-149584, No. 10-157293, No. 10-157300, No. 10-157301, No. 10-157302, No. 10-181199, No. 10-181201, No. 10-181203, No. 10-181206, No. 10-188340, No. 10-188341, No. 10-188358, No. 10-208303, No. 10-214423, No. 10-228671, No. 10-36693, No. 11-12483, No. 11-28865, No. 11-42858, No. 11-138999, No. 11-151861, No. 11-208111, No. 2000-318311 and No. 2001-80211
Those using a styryl dye and a metal reflective layer as recording materials: JP-A No. 10-151854, No. 10-188338, No. 11-34489, No. 11-99746, No. 11-99747, No. 11-144313 and No. 11-165466
Those using a formazan dye and a metal reflective layer as recording materials: Japanese Patent (JP-B) No. 2791944; JP-A No. 08-295079, No. 09-095520, No. 09-193546, No. 10-151862, No. 10-151863, No. 10-152623, No. 10-154350 and No. 10-337958
Those using a squarylium dye and a metal reflective layer as recording materials: JP-A No. 2001-322356
Those using a formazan-metal chelate compound, a squarylium-metal chelate compound and a metal reflective layer as recording materials: JP-A No. 2002-370451
Those using another dye and a metal reflective layer as recording materials: JP-A No. 10-86517, No. 10-226172, No. 10-244752, No. 10-287819, No. 10-297103, No. 10-309871, No. 10-309872
Those using an azo-metal chelate anionic dye and a cyanine cationic dye as recording materials: International Publication No. WO 98/29257; JP-A No. 11-34499, No. 11-195242, No. 11-250505, No. 2000-168237, No. 2000-190641, No. 2000-190642, No. 2000-198273 and No. 2001-67732
However, these materials have varying properties largely depending on wavelengths, since the resulting dye media are designed so as to have a recording-reading wavelength at a longer-wavelength-side end of an absorption band of the dye film to thereby yield their high reflectance (FIG. 1). Semiconductor laser for use in recording DVD drives has a varying oscillation wavelength depending on operating conditions. In particular, the oscillation wavelength shifts to a longer wavelength at high temperatures, thus inviting a decreased extinction coefficient “k” of the dye material used in the recording layer and leading to an insufficient recording sensitivity.
Objects and Advantages
Accordingly, an object of the present invention is to provide an optical recording medium that is applicable to recordable DVD systems using semiconductor laser having an oscillation wavelength shorter than those of conventional equivalents. Another object of the present invention is to provide such an optical recording medium having properties less dependent on a varying recording wavelength. Still another object of the present invention is to provide an optical recording method and device using the optical recording medium.